CA1212235A - Glass-melting furnaces - Google Patents

Abstract

Abstract of the Disclosure In a glass-melting furnace, electrodes and other devices may be protected from degradation by oxygen above an oxidation temperature thereof by immersion into the glass.
In such a glass-melting furnace, electrodes are inserted through the batch in symmetrical locations spaced from sidewalls of the furnace. Melting and refining takes place in relatively narrow bands below the watch.

Description

GLASS-MELTING FUl~ACES

Background of the Invention This invention relates to glass-melting furnaces. More particularly, the invention relates to the use of electrodes or other devices inserted at selected locations through the batch of a vertical glass-melting furnace.
In an electric glass-melting furnace, electrodes are coupled to a source of electrical power and placed in contact with a bath of molten glass. Electrical energy flows between the electrodes and dissipates energy in the form of Joule heating in the molten glass for melting a blanket of glass-forming batch materials deposited on and floating atop the bath. Such electrodes may be inserted through openings in - wall portions of the furnace as in conventional furnaces or may be directly placed in contact with the molten glass from above or through the layer of batch floating thereon as in the case of a cold crown electric melter.
A significant characteristic of a cold crown vertical furnace is its relatively great depth, e.g., 10'-15'. This depth is required in order to produce a specific convection pattern. An exemplary convection pattern comprises rapidly moving glass in the upper 2/3 of the furnace, sometimes hereinafter referred to as the active zone, and slower moving glass in the lower 1/3 of the furnace, sometimes hereinafter referred to as the quiescent zone. Such an arrangement gives the furnace the ability to produce quality glass at high melting rates. The present invention allows for the use of a relatively shallow furnace structure.
In conventional vertical furnaces, electrodes are located at the upper part of the walls near the batch :1~122~S

blanket. Introduction of the power close to the wall causes the hottest spot in the furnace to be at the wall. As a result, the furnace suffers from high corrosion rates and a short life.
Another problem with conventional vertical furnaces is that the electrodes suffer from high corrosion and short life. The electrodes project horizontally through the furnace sidewall, and may consist of three rods with the lateral surface area oriented perpendicular to the path of electrical current flowing there between. Thus, corrosion is concentrated at the tip of the electrode.
In prior art furnaces, the depth of the furnace must be increased as one increases the diameter. This is partly the result of the electrical power being dissipated close to the walls so that the center of the furnace is much cooler and produces a strong downward convection which in turn reduces the thickness of the quiescent zone.
In general, electrodes positioned through the batch have the advantage of being radially and vertically adjustable within the batch blanket on the top surface of the furnace.
This adjustability allows optimization of furnace performance for a particular output.
Batch electrodes are also more easily replaced than electrodes which extend through openings in the furnace sidewall. Consequently, the furnace is more reliable.
Also, the batch electrode rod is now vertically placed within the furnace. With electrical current uniformly placed over the side of the rod, the corrosion of the elect trove is minimized and electrode life increased.
Batch electrodes can be placed in a wide variety of positions. In general, these positions will coincide with the electrical phases available in a manner that symmetry of

2~35 current flow from the electrodes it maintained. Symmetry of electrical placement and firing are important and have been found to favorably affect melting efficiency and enhance furnace life.
In many glass-melting furnaces molybdenum Molly) it used as the preferred electrode material. However, because molt has a relatively low oxidation temperature of about 500~,C, complex protection devices are required to shield the electrodes from deterioration by contact with oxygen trapped in the glass-forming batch materials and/or other corrosive agents therein. Such devices include conventional water-cooled stainless steel sleeves or specially fabricated glass contact refractory sleeves which surround the electrode.
These devices are expensive and somewhat short lived. For example, water cooling tends to dissipate energy intended for glass-melting purposes and has a deleterious effect on melting efficiency and glass quality. Protection devices tend to be heavy and cumbersome and are not easily adjusted or replaced, thereby diminishing their versatility. Glass quality may also be affected by contamination of the glass by materials forming the protective devices which materials eventually corrode and become mixed with the glass in the furnace.
A preferred embodiment of the present invention utilizes a relatively inexpensive and long-lived system for directly immersing molt rods into a bath of thermoplastic material.
The molt rods are protected from oxidation without comply-acted peripheral apparatus. The system requires no cooling, and thus, energy utilization is enhanced. Further, the molt rods are supported in a relatively simple holder thereby facilitating adjustment and replacement.

It should be realized that the present invention is also applicable to other devices which may be directly immersed in a bath of molten glass as, for example, stirring devices, oxygen sensors and thermocouples. Also other oxidizable materials are contemplated ego. tungsten, rhenium, columbium, etc.), as long as the oxidizable portions thereof are protected in the manner set forth herein.
However, in order to simplify the disclosure herein, reference will mainly be made to the advantages of the present invention relative to molt electrodes. It is intended, however, that such other alternatives are to be considered part of the invention.

Summary of the Invention A method and apparatus is set forth for operating a glass-melting furnace having sidewall portions and a bottom wall forming a relatively shallow vessel for containing a bath of molten glass, wherein the furnace is electrically fired by at least one group of oxidizable electrodes inserted directly into the bath. The method includes the steps of placing each group of electrodes at selected locations about the furnace in a symmetrical circumferential pattern about a geometric center thereof, adjusting each group of placed electrodes to radial locations relative to said center which locations are relatively uniformly spaced from the center and at least a selected minimum distance from a sidewall portion of said furnace. Each electrode in a group is electrically fired in a symmetrical electrical pattern relative to each electrode in the group and each other group of electrodes such that heat energy within the furnace is concentrated away from the sidewall portions of the furnace.
The number of electrodes and dimensions of the furnace are chosen such that melting and refining of glass occurs within respective relatively narrow band below an upper surface of - the bath.
A method is also set forth for protecting or shielding dyes adapted to be directly inserted within a bath of molten glass. The method includes the steps of dipping the device into the bath of molten glass along a selected axial length thereof to a dipping level, allowing the molten glass to adhere to the device over said selected length and with-drawing the device and adhered molten glass from the bath at least to a selected operating level above the lower immersion level, such that portions of the electrode experiencing temperatures in excel s of an oxidation temperature thereof are coated with a layer of highly viscous, partially ~olidif ted glass .
The present invention also provides for a device for immersion into a supply of glass in a molten state, said device capable of operating in excess of an oxidation temperature thereof comprising: an oxidizable rod of a selected length having a tip end and extending axially therefrom to at least a support portion thereof, said rod being oxidizable in the presence of oxygen and at temperatures necessary to melt the glass, said rod being locatable in said furnace and partially submergible in he molten glass from the tip end to at least near the support portion thereof, a relatively thin coating of vitreous material adhered to a selected portion of the rod between the tip end and the support portion, said vitreous coating being relatively highly viscous at temperatures at least near said oxidation temperature of said rod and remaining adhered to said rod, and said rod being shielded from oxygen by said Catalina where the temperature of said rod is in excess of the oxidation temperature thereof..
A further aspect of the present invention is a method of protecting or shielding a device from oxygen within a glass-melting furnace containing a supply of molten glass, the device being maintained at elevated temperatures above an oxidizing temperature thereof comprising the steps of:
dipping the device into the molten glass to a selected immersion level along a selected length thereof susceptible to temperatures in excess of the oxidation temperature, maintaining the device at the immersion level a sufficient time in order to allow the molten glass to adhere to and coat the device over said selected length, and withdrawing the device and the adhered molten glass coating same from the bath at least to a selected operating level above the immersion level such that the device is shielded from oxidizing agents along the selected length.
Description of the Drawing Figure 1 it a schematic side sectional ill traction ox a preferred embodiment of a glass-melting furnace of the present invention including one exemplary batch electrode.
Figure 2 it a schematic top plan view of a typical electrode layout for the furnace of Figure 1 including a physics diagram superimposed thereon.
Figure 3 is a plot of furnace height versus melting area for furnace with and without batch electrodes.
Figure 4 it a fragmented schematic idea sectional illustration of an electrode (including a phantom view thereof) immersed in a glass-melting furnace being orated it accordance with the principle of the prevent invention.
Figure PA i schematic diagram illustrating an inclined electrode.

-pa-Figure 5 is a schematic illustration of an alternate embodiment of an electrode constructed in accordance with the principles of the present invention utilizing a graded glass shielding device.
Figure 6 shows another embodiment of the present invent toil wherein the electrode has an axial opening into which a purge fluid is introduced.

Description of the Preferred Embodiments Figure 1 shows a preferred embodiment of a vertical electric glass-melting furnace 10 of the present invention illustrated schematically in side section with cross hatching eliminated for clarity. Preferably the furnace 10 is polyp gonad or near circular having a geometric center C and radius R (see Fig. 2). The furnace 10 includes an upstanding sidewall 14 and a bottom wall 16 having an outlet opening 15 at center C. The furnace 10 contains a bath of molten thermoplastic material such as glass 12. The bath of molten glass 12 has a upper surface 18 upon which there it deposited a quantity of glass-forming batch materials or batch 20.
The batch 20 is in the form of a floating blanket which insulates the surface 18 of the bath 12 and retains heat within the furnace 10. The molten glass 12 is initially melted by conventional means including a gas burner (not shown). Thereafter continuous melting takes place by means of one or more groups of current-carrying electrodes 30 (subscripts sometimes omitted) inserted into the bath 12.
Electrodes 30 closes and the sidewall 14 are labeled with the designation O for outer and the electrodes 30 closest the center C are labeled I for inner.
Each electrode 30 may be carried by suitable means not shown herein but clearly disclosed in any one of the above 9 'I

referred to US. patent applications. The electrodes 30 are free to he moved vertically, radially, circumferential and angularly. Radial positioning of the electrodes 30 is especially important for maintaining proper heat distribution.
The outer electrodes 30-0 are placed no closer to the sidewall 14 than a selected minimum spacing or distance S. Heat energy produced by outer electrodes 30-0 is removed from sidewalls 14 rendering the same relatively cool in comparison to prior art furnaces.
It is well known that a temperature gradient in a glass melting furnace causes the glass to move in convective rolls. In one embodiment of the present invention it is preferred that the electrodes 30 produce heat directly under the batch blanket 20. The outer electrodes 30-O are fired with a greater power to produce more heat about the periphery of the furnace 10. The glass 12 in the furnace tends to move radially inwardly of the furnace and downwardly near the center C which is relatively cooler. The glass 12 moves in a convective roll pattern as hereafter described. The convective roll TV (see arrows) circulates across upper part of the furnace near the upper surface 18 radially inwardly towards center C, thence downwardly near the center towards an interface 21 separating upper active zone A from lower quiescent zone Q. The glass 12 meets the boundary 21 and tends to move radially outwardly from center C to sidewalls 14. Thereafter the glass 12 moves downwardly along sidewalls 14 towards bottom 16 and thence radially inwardly across bottom 16 towards the center C and to outlet 15.
The convective roll TV shown represents the path taken by freshly melted glass 12 having a minimum residence time in the furnace 10 necessary to produce good quality product.

It should be clear that some of the glass 12 recirculates in lZ~235 the furnace 10 and has a longer residence time. Also, other patterns are possible. For example, in a furnace having a refractory metal liner, the outer electrodes 30-0 may be run cooler than the inner electrodes 30-I creating a "C" convection pattern. The glass would move along the top of the furnace, from the center C to sidewalls 14 and thence downwardly towards bottom 16 and across inwardly to central outlet 15.
The "C" pattern provides for a shorter residence time.
However, in a lined furnace this may be compensated for by running the furnace at a higher temperature such that high quality glass may be produced.
The power applied to the outer electrodes 30-0 and minimum spacing thereof from sidewalls 14 is important for controlling the velocity and direction of the convective roll TV. Hot glass 12 tends to remain high in the furnace 12 and cool glass 12 tends to descend. The relative dip-furriness in glass temperature thus governs the raze at which glass 12 rises or descends in the furnace 10. If the outer electrodes 30-0 are overpowered or placed too close to the sidewalls 14, heat energy concentrated at the electrodes 30-0 will cause overheating and rapid corrosion of the sidewalls 14. Further, the flow of convective roll TV may be disrupted.
Thus, the glass 12 may follow a path to outlet 15 which does not provide sufficient residence time to produce good quality glass. If the outer electrodes 39-0 are far removed from sidewalls 14 a fast downward flow may occur near said side-walls causing reduced residence time and increased furnace wear. Properly placed outer electrodes 30-0 control the speed of the convective roll TV without overheating the sidewalls 14.
The furnace 10 has two major vertical zones. Initial melting of batch 20 takes place in the upper portion of the furnace 10, herein before referred to as the active zone A.
Fining takes place in lower portion of the furnace referred to as the quiescent zone Q. The respective active and quiescent zones A and Q are shown schematically separated by the dotted line 21.
In Figure 1, the sidewalls 14 are shown as extending above the upper surface 18 of the glass 12. However, for purposes of discussion herein, the furnace can be said to have a height, depth or vertical dimension H as shown extend-in across the respective active and quiescent zones A and. This dimension does not necessarily include a sup (not shown) present in some furnaces.
Although the furnace may be constructed in various shapes and sizes, for purposes of simplifying the discussion and analysis herein, the furnace 10 may be considered to be circular having radius R as lateral dimension measured from the center to an interior surface 27 of sidewall 14. For near circular shapes the lateral dimension should be considered the shortest distance from the center line to the sidewall (for example, assuming a regular polygon: the short per pen-declare to a side.) In non circular arrangements the longer dimension should control (for example one half the width of a rectangle or the focal length of an ellipse). In the disk cushion below, near circular shapes are emphasized because they are believed to be most efficient.
Figure 3 illustrates that a furnace 10 having batch electrodes may be significantly reduced in depth. Curve A

shows the relation of depth versus surface area in a vertical refractory furnace with wall electrodes. Curve B show the relation for the same type of furnace with batch electrodes.

The curves are relatively close together for small furnaces twig. less than 25 ft2). However as the furnace size s increases the curves follow similar but offset path. For example, in furnaces having a melting area of between about 100 and 300 ft2 the furnace with batch electrodes may be about 2 ft. lower in depth. This is a significant reduction in depth which results in lower construction cost. The operating cost of such a furnace is also reduced due to lower heat loss for the smaller sidewall surface area.
Notice that except for relatively small furnaces the depth should exceed at least 4' overall. In the range 100 ft2-300 ft2 plus, the depth of a furnace without batch electrodes increases to about 10 ft., including a 3' quiescent zone Q.
In the same range a furnace with batch electrodes has a depth of about 8 ft. and a similar quiescent zone. The same quiescent zone is needed to refine the glass but a shallower active zone is needed for melting because of the improved efficiency of batch electrodes.
In a typical furnace made and operated in accordance with the present invention, an aspect ratio thereof Jay be defined as the vertical dimension H divided by the lateral dimension equal to the diameter D or twice the radius R. In a small furnace where D is about 5 feet or less the aspect ratio should not be less than about 1Ø As the diameter D
increases, the aspect ratio should follow curve B in Figure

3 to about 0.3. It should be understood however, that the shallowest furnace is desired for the particular lateral dimension chosen. Further, the dimensions should be chosen to minimize energy losses as much as possible.
In Figure 2 there is shown a top plan view schematically illustrating a typical electrode layout for the furnace 10 of Figure 1. In a furnace of the type herein described, two sets of electrodes are set out. A first set or group of six main electrodes TOM are located along radial lines at 60~

intervals or positions (lM-6M) about the center C of the furnace 10. The main electrodes or mains 30M may be located at some radial position RUM from the center C of furnace 10 The mains 30M (shown as dark circles) may be electrically energized by a source ox power (not shown) in a cross fired arrangement producing fussers PM. A second set of six pairs of respective inner and outer staggered electrodes SUE, SUE shown as open circles, are interspersed at six toga-lions lS-6S circumferential half-way between the main electrodes 30M. Similarly, the respective inner and outer staggered electrodes SUE and SUE may be located at respective radial positions RS-I and RHO Staggered elect troves 30S-0 and SUE when energized produce a pair of fuzzier PUS adjacent and in the same sense as each main fuzzier PM. Other possible arrangement also include aligning inner electrode SUE in line with mains 30M and cross fired.
Also inner electrode SUE could be placed intermediate mains TOM and outer electrode SUE and independently fired.
In Figures 1 and 2, assuming a substantially circular furnace 10 of radius R and depth H, the following are examples of electrode positions for various nominally sized furnace:
Example I
Furnace Radius R = 10' Furnace Depth H = 7.5' No. Electrodes = 15-18 six (6) mains 30M
six (6) outer staggered SUE
three (3) to six (6) inner staggered SUE
Location Radius Angle between Position E eastwards 30M RUM = 9' 60 lM-6M

30S-0 RHO = 9' 60~ lS-6S
(offset from mains by 30) SUE RSI = 3-5 120-60 on line with outer staggered electrodes :l~lZ;~35 Spacing S from sidewall 14 = minimum 1' all electrodes Example II
Furnace Radius R = 5' Furnace Depth H = 5' No. Electrodes = 9 six (6) mains 30M
three (3) staggered (inner) Location Radius Ankle between Position Electrodes 30M RUM = Al 60~ lM-6M
SUE RUM = 1.5-2 120 US, US, US

Spacing S from sidewall 14 = minimum 1' all electrodes Example III
Furnace Radius R = 2.5' Furnace Depth H = 3' No. Electrodes = 3, 4 or 6 Position - RUM = US - 1.5-2.0 Angle - 120, 90, or 60 Spacing S from sidewall 14 - minimum 1' all electrodes In the present invention batch electrodes 30 subscripts sometimes hereinafter omitted ma be set up as in Example I
spaced from sidewalls 14 and placed along radial lines at 30 intervals. The radial position of each batch electrode 30 is a significant variable. Notice that batch electrodes 30 may be placed near the center C or near the sidewall 14 and that there may be more than one batch electrode 30 on any radial line. Further it is possible to provide symmetric eel placement locations, such that, no two electrodes lie on the same radial line. By placing electrode 30 in these positions, electrical symmetry of current flow is maintained.

Inner staggered electrodes SUE placed near the center C of the furnace 10 (e.g., at RS-I = R/2 or Lucas, have two advantages. First, by providing power in the center C of the furnace 10, the melting rate in the center can be increased.
In conventional furnaces the center ordinarily has the lowest melting rate since it is furthest from wall electrodes.
By placing electrodes 30-I near the center, either the output of the furnace 10 can be increased or the wall them-portray can be reduced.
A second advantage of placing inner staggered electrodes SUE near the center C of the furnace 10 is that the furnace 10 need not be as deep. Power concentrates near the underside 20' of the batch blanket 20 in the active zone A where melting is desired (see Figure 1). Concentrating power near the batch blanket 20 tends to produce a relatively stable quiescent zone Q in about the lower 1/3 to 1/2 of the furnace 10. Ideally, the glass 12 in the quiescent zone Q tend to move slowly towards outlet 15 thereby providing sufficient residence time for the glass 12 to fine.
The placement ox main electrodes 30M and outer staggered electrodes SUE near, but spaced from the sidewall 14 of the furnace 10 has significant advantages in addition to those set forth above. The number of electrodes can b greatly reduced since there is better utilization of elect trove surface area. That is, significant current slows from lateral spaces 30 of electrodes 30 rather than from tip 31. For example, in a conventional furnace having a radius of 10', forty-eight I electrodes are used With the present invention, electrode usage could be reduced to between twelve (12) and eighteen lo electrodes.
In a large furnace having a diameter greater than about 5', batch electrodes 30 are placed around the periphery of ;235 the furnace 10 spaced from sidewall 14 by about 1-2 feet as well as near the center C thereof. By eliminating convent tonal wall electrodes and spacing electrodes 30M and SUE
I feet from the wall, the temperature of the sidewall 14 and hence corrosion of the refractory, can be greatly reduced.
In a small furnace 10, electrodes 30 should be placed closer than 1' to the sidewall in order to produce the desired "S"
convection. If a "C" pattern is desired, the electrodes 30 could be placed at about R/2.
The invention operates as follows: At least one group of electrodes 30 are arranged in a pattern, one each in a selected position of the pattern relative to the geometric center C of the furnace 10. The pattern is symmetrical in radial and circumferential directions relative to the center C. Except for small furnaces placement of the electrodes 30 near the sidewalls is restricted to not closer than about 1 foot. Each electrode 30 or groups of electrodes may be carried separately by a dedicated support arm or other suitable device (not shown). Likewise, different ones of the various groups of electrodes 30 may be carried on a common support (also not shown). Thereafter, the electrodes 30 are then lowered into the furnace 10 through the batch blanket 20 and energized. Energization of the electrodes should be symmetrical with each electrode in a group dissipating substantially the same energy as other ones in the group.
The preferred embodiment seeks to produce uniform melting across the furnace with relatively high heat near but spaced from sidewalls 14 and somewhat lesser heat concentrated at the center C. Of course, other arrangements of electrical firing are possible and such should be tailored to the idiosyncrasies of the furnace 10 to provide a heat distribution, which while not totally uniform, produces good quality Z~'~23~
glass.
The electrodes 30 may be operated with their tips 31 at a selected operating depth DO below the upper surface 18 of glass 12. Further, the depth ox one group of electrodes, e.g., the mains 30M in Figure 2, may be different than the depth of the staggered electrodes SUE and SUE. Also, adjustments may be made to vary the depth of individual electrodes if desired. However, for purposes of illustra-lion herein, the operating depth DO of all the electrodes 30 is assumed to be the same and substantially constant once determined.
The drawing of Figure 3 illustrates curves for relatively clear glasses. Such glasses tend to require a relatively thick active zone A because energy radiates toward the bottom 16 preventing the thermal stratification that pro-dupes a clearly defined quiescent zone Q. The temperature difference between the upper surface 18 of the glass 12 and the furnace bottom 16 may be as small as 25~C. The furnace - must be deep enough to produce relatively distinct active and quiescent zones. Other so-called dark glasses tend to suppress radiation The active and quiescent zones are probably more distinct and both Jay by somewhat narrower than in a furnace melting clear glass. The drawing of Figure 3 represents the case where active and passive zones are broadest. It should be apparent that, except for small furnaces, the overall height of furnaces operated in accord-ante with the present invention may be reduced by about 2 feet.
For the clear glasses the tip 31 of the electrodes 30 should be placed as close to an underside 20' of the batch 20 without exceeding current density limits or creating hot spots in the blanket. The operating depth DO of each elect trove 30 may be changed by mean set forth in the above noted patent application and are not detailed herein. It can be readily appreciated that since adjustments to the operating depth DO are easily accomplished, adjustment of the operating characteristics of the furnace it facilitated.
More efficient melting can be achieved because the location of the tip end 31 of each electrode 30 can be adjusted to best suit melting characteristics of the particular glass being melted.
Figure 4 illustrates another embodiment to the present invention wherein a vertical electric glass-melting furnace 110 is illustrated in fragmented side section. The furnace 110 contains a bath of molten thermoplastic material such as glass 112. The furnace 110 includes an upstanding side wall 114 and a bottom wall 116. The bath of molten glass 112 has an upper free surface 118 upon which there is deposited a quantity of glass-forming batch materials or batch 120. The batch 120 is in the form of a floating blanket which insulates the free surface 118 of the bath 112 and retains heat within the furnace 110. The molten glass 112 is initially melted by conventional means including a gas burner not shown.
Thereafter, continuous melting takes place by means of a plurality of current-carrying electrodes 130 inserted into the bath 112. Only on electrode 130 is shown in order to simplify the drawing.
Each electrode 130 may be carried in a collar 134 secured to a support arm structure 132. The collar 134 has an adjustment ring structure 136 for allowing the electrode 130 to slide up and down within a through opening 138 in - 30 said collar 134. The support arm 132 is shown fragmented and is suitably supported exterior of the furnace 110 by a frame structure (not shown) which allows the support arm 132 SWISS

to move upwardly and downwardly in the direction of the double headed arrow A in Figure 4. Support arm 132 may be joined to collar 134 by sleeve 135 which allows individual placement of electrode 130 (see curved double headed arrow B). Also, support arm may be moved circumferential about its frame structure by means not shown (in the direction into and out of the page as illustrated by double headed arrow C.) Although other aspects and embodiments are described herein, the present invention it primarily concerned with protecting the electrode from its tip 131 to a point there-along at 133 just below the collar 134. The electrode 130 is normally i~nersed so that its zip end 131 extend into the bath 112 to a depth Do, referred to as the operating level, as measured from the free surface 118. In the phantom drawing, superimposed on the solid line drawing in Figure 4, electrode 130 is shown with its tip 131 immersed to a second or dipping level Do as measured from the tree surface 118 of the bath of glass 112.
The invention operates as follows: a portion of the electrode 130 from the tip 131 to near the point 133 is submerged or dipped into the bath 112. The electrode is held submerged with its tip 131 at the depth Do for several minutes until it becomes heated sufficiently, Such that, the glass 123 becomes adhered to the electrode 130 at least along a portion thereof submerged below the free surface 118 (i.e. from tip 131 to near point 133). After sufficient time has elapsed for the molten glass 112 to adhere to the electrode 130, it is partially withdrawn from the furnace 110 up to the operating level Do. Adhered glass shown at reference numeral 140 forms a coating 140 having respective upper and lower edges AHAB. The coating 140 covers or coats a selected length L of the electrode 130 as a relatively 1~2~3~

thin film of thickness t thereby blocking oxygen inflator-lion and protecting the electrode from deleterious oxidation.
The thickness t of the coating 140 is dependent upon the temperature and viscosity characteristics of the glass 112.
The adhered glass coating 140 becomes partially solidified or highly viscous due to the fact that the temperature of the electrode 130 drops to near a solidification temperature thereof as one moves away from the tip 131. Also, the batch 120 surrounding the electrode 130 is relatively cool and insulates the coating 140 prom the high heat of furnace 110.
The depth at which the electrode 130 is operated may vary about the depth of Do, but for purposes of illustration herein, the operating level Do of the electrode 130 remain substantially constant once it is determined. External cooling of the electrode 130 is not generally necessary since portions thereof above upper edge AYE which are exposed to ambient oxygen are cooled by natural convection to below the oxidation temperature of the molt. Portions ox the electrode 130 below a-lower edge 140B of the coating 140 are protected from oxidation by immersion in the molter glass 112.
The present invention has most significant applications for batch electrodes or electrodes which penetrate a batch blanket in cold crown vertical melters. In principle, however, there is no reason why such an electrode could not be utilized wherever electrodes are presently used in furnaces (e.g. through the side walls 114 or bottom wall 116) as long as some form of protection it provided to prevent furnace leaks.
The present invention affords considerable savings over conventional protective devices. Further, since conventional devices are typically water cooled, there are significant energy savings available resulting in higher melting effi-shanties.
For certain glasses the tip 131 of the electrode 130 should be placed as close as possible to an underside 120' of the batch 120 near free surface 118. For other glasses more efficient melting takes place when the tip 131 of the electrode 130 is placed further down in the molten glass 112. It can be readily appreciated that these adjustment are more easily accomplished by utilization of a bare rod concept herein described. Since the electrode structure formed of a cylindrical molt rod is significantly lighter without the stainless steel water-cooled jacket of the prior conventional furnaces, adjustment of operating level Do of the electrode 130 is uncomplicated. Thus, more efficient melting can be achieved because the location of the tip end 131 of the electrode 130 can be fine tuned to best suit melting characteristics ox the particular glass being molted.
The operating level Do of the electrode 130 may be changed by simply moving the support arm 13~ upwardly and/or downwardly from exterior the furnace 110 or by moving the electrode in support collar 134. Further, the electrode 130 may be reciprocated between levels Do and Do to periodically replenish the coating 140.
The outer surface of the electrode 130 may be treated prior to immersion in the bath 112 in order to protect the molt and to allow for more adequate adhesion of the glass layer 140 to the electrode 130. A refractory substance such as a flame sprayed aluminum oxide sold under the trademark WRECKED appears to reduce oxygen contamination and has a beneficial effect on adhesion of the glass layer 140 to the electrode 130. coating of chromium oxide o'er the surface of electrode 130 may also enhance adhesion of the glass I

coating 140. It has been found that slight oxidation of the electrode 130 itself may be helpful to glass adhesion. A
coating of molybdenum dieselized may also be used to protect the electrode 130 from oxidation.
Sometimes gases are evolved during the glass melting process (see Figure PA). If such gases come into contact with the electrode 130, oxidation or corrosion thereof may occur. As a further precaution against oxidation, there-fore, the electrode 130 may be inclined about the vertical by means of sleeve connection 135 lee double headed arrow B). Gas bubbles evolved will tend to float vertically upward and away from electrode 130.
In Figure 5 there is illustrated an alternative embody-mint of the present invention wherein electrode 130' is pro-shielded with a protective glass coating 140'. The electrode 130' has a molt collar 135 located near the tip end 131.
The collar 135 may be threaded, shrink fit or bolted onto the electrode 130'. A plurality ox different glass-~orming materials, in the form of unconsolidated gullet or solid glass annular rings or annular cylinders EYE, may be located axially of the electrode 130' along a selected length L' to grade the protective coating 140' thereof. If glass gullet is utilized for the rings AYE, an alumina tube 139 of sufficient length may be joined at a lower end 141 to the collar 135 for containing the materials therein.
A fused silica material such as sold under the trademark VICAR could be used for tube 139. At an upper end 143 of the tube 139, an annular refractory cap or plug 145 may be sleeved over the rod 130' and located within the tube 139 to close a space containing the protective coating 140' therein.
The plug 145 may be a packing material such as FIBERFRAX3 Rope. Additionally, a readily available extrudable silicone c sealant 147 such as Dow Corning REV 732 could be placed over refractory cap 145. A purge line 14~ may be fitted through opening 149 in plug 145 and goal 147 for the introduction of a purge gas P interior the tube 139. A purge gas P protects the molt electrode during startup before the gullet rings AYE melt. Thereafter, the molted material protects electrode from oxygen contamination.
The electrode 130' illustrated in Figure 5 might be suitably clamped to the support collar 134 and slowly lowered lo through the batch 120 and into the molten glass 112. At such time, the various layers of protective materials AYE
would become melted or softened and adhere to the electrode 130'. It should be realized that, as in the embodiment of Figure 4, the protective layer 140 experiences a temperature gradient when placed in service. The temperature of the electrode 130' decreases as one moves axially thrilling from the tip 131 to he point 133 near where it is supported by collar 134. Different glass compositions may he used for the rings AYE forming protective layer 140', each having a different softening and annealing point. Each will be susceptible to some viscous flow at various temperatures.
By tailoring the compositions of rings AYE prom relatively hard glasses, for the lowest protective layer AYE near the tip 131, to relatively soft glasses at the upper end of the protective layer 133, each will exhibit the proper character-is tics at its anticipated operating temperature. By grading the glasses as hereinabove set forth, there is less likely-hood of thermally shocking the protective layer 140' over the temperature gradient thrilling. Further, because the batch layer 120 acts as an insulator from the high heat generated within the bath of molten glass 11~, the protective coating 1401 will remain relatively intact even though it is ~Z235 softened.
The following Example is thought to set forth a suitable embodiment of a graded protective coating 140' beginning with the lower ring AYE or relatively softer glass and progressing to the uppermost ring EYE of relatively harder glass as follows:
AYE - Borosilicate (Corning Code 7740) (8" long) 137B Alkali Barium Borosilicate (Corning Code 7052) (7" long) 137C - Borosilicate having a high boric oxide content as set forth in US. Patent 2,106,744 DOW - Borosilicate glass as in 137C mixed with increasing amounts of an hydrous boric oxide from 20 to 40% respectively (I" long each) Rings AYE - 100 mesh gullet Tube 139 - VYCOR*brand tubing Total length of coating - approximately 36"

The present invention also contemplates the use of a borosilicate glass tube 139 such as Corning Code 7052 having an expansion comparable with the molt. The tube 139 would be sealed directly to the electrode 130' without the gullet fill AYE. The electrode 130' should be preheated in order to prevent thermal shock.
An advantage of the arrangement illustrated in Figure 5 is that electrode 130' may be prefabricated for quick insertion into the furnace 110 without any other preparation.
The tube 139 not only contains there within the protective layer 140' (if in granular form, but also provides or some protection of the protective layer 140' at least until it is consolidated during operation of the furnace 110~ The molt collar 135 would normally be located below the level of the free surface 118 of the bath 112 shown in Figure 4, and thus, is protected from oxidation by its immersion in the molten glass 112.

1;21~2~35 In Figure 6 there it illustrated yet another embodiment of the present invention. An electrode 130" may have an axial bore 150 drilled or formed therein. The bore 150 extends generally lengthwise thereof from an open upper end 151 to near tip 152 thereof. purge line 1~3 may be located in the open end 151 and a purge fluid P introduced therein.
At elevated temperatures, hydrogen or other gases inert with respect to molt will diffuse there through as shown by dotted arrow Pd. This embodiment, when dipped, as shown in Figure 1 or otherwise protected from oxidation as elsewhere set forth herein, is additionally protected from oxidation without undue energy and materials costs.
While there has been described what are considered to be the preferred embodiments of the present invention it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from to invention, and it is intended in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

Claims (18)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of protecting or shielding a device from oxygen within a glass-melting furnace containing a supply of molten glass, the device being maintained at elevated temperature above an oxidizing temperature thereof comprising the steps of: dipping the device into the molten glass to a selected immersion level along a selected length thereof susceptible to temperatures in excess of the oxidation temperature, maintaining the device at the immersion level a sufficient time in order to allow the molten glass to adhere to and coat the device over said selected length, and withdrawing the device and the adhered molten glass coating same from the bath at least to a selected operating level above the immersion level such that the device is shielded from oxidizing agents along the selected length.

2. A method as set forth in claim 1 wherein the device comprises at least one of an electrode, thermocouple, oxygen sensor and stirrer.

3. A method as set forth in claim 1 further comprising the step of electrically energizing the electrode for con-ducting electrical currents through the bath of molten glass.

4. A method as set forth in claim 3 wherein evolved gases occur adjacent the energized electrode and further including the step of inclining the electrode relative to a vertical direction in order to minimize contact of the evolved gas and the electrode.

5. A method as set forth in claim 1 further comprising the step of precoating the device with an annular glass coating at least along the selected length.

6. A method as set forth in claim 5 wherein the step of precoating comprises the steps of: selecting at least one vitreous material, surrounding the device therewith along the selected length.

7. A method as set forth in claim 6 wherein selecting the vitreous material comprises the step of choosing a plurality of vitreous materials having different viscosity character-istics from a relatively hard glass to a relatively soft glass and locating said materials about the device in axially located annular bands from the respective relatively hard to soft glasses beginning near a portion of the device exposed to relatively higher temperatures for avoiding thermal shock and spalling of the vitreous materials away from the device.

8. A method as set forth in claim 6 wherein the vitreous material is initially in granular form and the method further comprises the step of containing the granular vitreous material in position about the device until said vitreous material becomes softened and viscously adhered to the device.

9. A method as set forth in claim 8 further comprising the step of sealing the contained granular material against ambient atmosphere.

10. A method as set forth in claim 8 further comprising the step of introducing a purge gas through the granular material adjacent the exterior of the device.

11. A method as set forth in claim 1 further comprising the step of diffusing a purge gas through the device from the interior to the exterior thereof.

12. A device for immersion into a supply of glass in a molten state, said device capable of operating in excess of an oxidation temperature thereof comprising: an oxidizable rod of a selected length having a tip end and extending axially therefrom to at least a support portion thereof, said rod being oxidizable in the presence of oxygen and at temperatures necessary to melt the glass, said rod being locatable in said furnace and partially submergeable in the molten glass from the tip end to at least near the support portion thereof, a relatively thin coating of vitreous material adhered to a selected portion of the rod between the tip end and the support portion, said vitreous coating being relatively highly viscous at temperatures at least near said oxidation temperature of said rod and remaining adhered to said rod, and said rod being shielded from oxygen by said coating where the temperature of said rod is in excess of the oxidation temperature thereof.

13. An device as defined in claim 12 wherein the coating comprises a semi-solidified mass of the supply of glass forming a viscous film about the electrode from at least the upper free surface of the glass to at least a portion or the electrode which has a temperature below the oxidation temperature of the device.

14. A device as defined in claim 12 wherein the coating comprises a plurality of annular formations of vitreous materials surrounding the device continuously along the selected length, said vitreous materials being formed of substances having viscosity characteristics successively ranging from a relatively high viscosity near the electrode tip to a relatively lower viscosity remote from said tip.

15. A device as defined in claim 13 further comprising: a lower support means secured to the device near the tip said support means engaging the high viscosity annular formation for supporting the coating against viscous flow thereof in the direction of the tip.

16. A device as defined in claim 14 further comprising an annular containment tube surrounding the device coating along the selected length thereof said tube being secured at one end to the support means for preventing flow of the coating away from the device.

17. A device as defined in claim 15 wherein the annular tube is formed of materials selected from the group consisting pri-marily of fused silica and alumina.

18. A device as defined in claim 12 further comprising means for introducing a purge gas into the same for shielding the device from deleterious ambiance.